Ripley's belt goes over the middle belt loop on the back of his white Levis about eight minutes into the film. A couple of minutes later, the belt goes through the loop, though the action was continuous, with no possibility of him having removed his belt to correct this fashion fumble.
The position of the boom on the sailboat is inconsistent.
The name of composer Nino Rota is misspelled "Nino Rotta" in the opening titles.
Onlookers are clearly visible in the background in the fish market scene.
During the medium shots of the boat, which is supposed to be sailing in isolation, the wake of the boat sailing next to it with the camera crew is clearly visible.
While sitting in a hotel room, Tom takes an envelope and licks it before putting it in his coat pocket. However, he never sealed the envelope and left the flap open.